Powdery mildew is one of the most common plant diseases in the garden. However, this is an infection with many different pathogens. Read about the measures and resources you can use to help your plants.

Powdery mildew can affect almost any plant

Table of Contents

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  1. the essentials in brief
  2. Powdery mildew or downy mildew?
  3. combat powdery mildew
  4. frequently asked Questions

    5. the essentials in brief

    • Differentiation between different highly contagious powdery mildew fungi: "fair weather powdery mildew" vs. "bad weather powdery mildew".
    • Cut back affected parts of the plant and treat the plant with fungicides.
    • In milder cases, proven home remedies such as B. Milk or baking soda.
    • To prevent this, ensure sufficient planting distance and never water plants from above.

    Powdery mildew or downy mildew?

    Powdery mildew is known to most hobby gardeners as a mealy-white, wipeable coating that affects almost all parts of the host plant and gradually spreads. However, it is not a single pathogen, instead the disease name is to be seen as a collective term for various fungi. A rough distinction is made between powdery mildew (pathogen: from the Erysiphaceae fungus family) and downy mildew (pathogen: from the Peronosporaceae fungus family).

    The different species of both families - some are quite specialized and only affect certain plant species such as apple powdery mildew - first attack the leaves and young plant shoots and buds. The fungus that grows on the surface deprives the plants of important nutrients and water, which is why the disease can lead to the death of the entire plant if left untreated. Many garden plants are afflicted by powdery mildew every year.

    powdery mildew Wrong mildew
    pathogen Ascomycota (Erysiphaceae) Egg mushrooms (Peronosporaceae)
    Look white, floury coating that can be wiped off, mainly on the upper side of the leaf, but also on other parts of the plant greyish coating on the underside of the leaf
    damage picture discoloration and drying up of plant parts and fruits, growth inhibitions up to the death of the plant discoloration and drying up of plant parts and fruits, growth inhibitions up to the death of the plant
    Appear "Fair weather fungus": occurs more frequently in dry and warm summer weather "Bad weather fungus": prefers humid weather with temperatures between 15 and 20 °C, greenhouse cultures are particularly at risk
    antidote Milk-water mixture, baking soda, garlic, horsetail Milk-water mixture, baking soda, tansy, nettle, oregano

    Powdery mildew - the "fair weather fungus"

    Powdery mildew tends to live on the leaf surface

    The powdery mildew fungi (lat. Erysiphaceae) are a family of fungi with around 19 genera, which in turn belong to the sac fungi (Ascomycota). Typical for these species is the occurrence as so-called ectoparasites, because they need a living plant as a host.

    However, powdery mildew fungi do not penetrate deep into the plant tissue - in contrast to other parasitic fungi - but form their mycelium, the fungal network, exclusively on the surfaces. Here the fungi form sucking appendages that bore into the outer leaf cells and thus provide the required nutrients and water.

    Due to the lack of water and nutrients, the affected plants wilt and eventually die. The fungi reproduce via spores, which are carried by wind and insects and can reproduce explosively in warm and dry weather. Powdery mildew occurs mainly on roses and grapevines, but can also affect other ornamental plants and crops, such as phlox or gooseberries.

    Downy mildew - the "bad weather fungus"

    “Never water garden plants from above! Too much moisture on the leaves favors powdery mildew.”

    On the other hand, the egg fungi (lat. Peronosporaceae), which belong to the downy mildew, are not real fungi from a botanical point of view, but are related to diatoms and brown algae. For this reason, they are also referred to as algae fungi. In contrast to powdery mildew, the pathogens in this group penetrate deep into the plant tissue and develop their fungal network between the plant cells.

    Downy mildew is actually an alga

    Characteristic of this form of powdery mildew is the greyish fungal growth that usually develops on the underside of the leaves. Only when the disease has progressed do yellowish to brownish, mosaic-like spots appear on the upper side of the leaves. Downy mildew prefers a warm, humid climate and therefore often occurs in greenhouses that are not adequately ventilated.

    A typical example of this plant disease is late blight in potatoes. But downy mildew can also occur on roses, vines, sunflowers and many other types of plants.

    How to distinguish between powdery and downy mildew at a glance:

    powdery mildew Wrong mildew
    white, mealy fungal growth on the upper side of the leaves greyish fungal growth on the underside of the leaves, later mosaic-like leaf spots
    prefers warm and dry weather prefers damp and warm (up to 20 °C) weather
    Mycelium does not penetrate plant tissues, remains on the surface Mycelium penetrates deep into the plant tissue

    Causes of Powdery Mildew

    But no matter what form of mildew it is, powdery mildew and downy mildew are very similar in terms of causes:

    • strong weather fluctuations, a. in the spring
    • improper watering (over the leaves instead of directly onto the ground)
    • wrong time to water (in the evening instead of in the morning)
    • Over-fertilization: nitrogenous instead of balanced fertilization
    • too narrow planting, planting distance not maintained
    • wrong location

    In particular, check endangered plants - some plant species are more susceptible to powdery mildew than others - regularly for the above signs of infection. Act as soon as possible at the first symptoms, as the disease spreads quickly. In addition, powdery mildew is more difficult to combat the further the disease has progressed.

    Effectively combat powdery mildew

    Powdery mildew should be combated as early as possible

    The best protection against powdery mildew is simply prevention. With a few measures you can reduce the risk of disease for your plants in the garden and greenhouse, so that the fungi do not even make themselves comfortable. However, this does not always work and in the event of an infection you have to resort to more severe measures.

    If you have discovered the disease at an early stage, you can fight it with various home remedies and biological, home-made pesticides. Some beneficial insects also eat the fungus, which is why they are ideal for use in rose beds. In the event of a severe infection, only garden shears and chemical fungicides can often help.

    When are which measures to combat powdery mildew useful? An overview

    • Preventive action: Sufficient planting distance, optimal location, planting of plants that protect against powdery mildew (basil, garlic), annual pruning (usually in spring), regular application of plant strengtheners (plant manure)
    • Mild mildew infestation: Household remedies (milk, baking soda), siliceous plant strengtheners (horsetail), mildew-eating beneficial insects, special microorganisms
    • Heavy mildew infestation: strong pruning, chemical pesticides based on copper or sulphur

    Timely pruning helps against powdery mildew

    Many gardens are afflicted by powdery mildew every year. You can contain this plague by cutting off the shoot tips of the affected plants every year in autumn and, if necessary, in summer or by cutting back vigorously in advance. This is where the mildew spores like to overwinter, only to appear again next spring.

    For the same reason, you should not leave fallen leaves and other infected plant parts lying around or even throw them on the compost. In general, if necessary, severe pruning of infested plants makes sense in order to counteract the spread of the fungal pathogen and to prevent it from the outset. In addition, once infected plant parts no longer take on a healthy colour, but simply retain the leaf spots, discolouration and dried-up areas.

    digression

    These plants are particularly susceptible to powdery mildew

    In addition to wine and roses, apple trees and tomatoes are particularly susceptible to powdery mildew. On the other hand, many crops, such as tomatoes, potatoes, cucumbers and other cucumber plants, lettuce, parsley, carrots, celery, strawberries and peas, often suffer from downy mildew.

    Home remedies help against mild infestations

    You don't have to bring out the heavy artillery in the event of a mild mildew infestation, because these toxins not only have negative effects on the fungal pathogens. Chemical fungicides only make sense after careful consideration of all the advantages and disadvantages if nothing helps at all. If mildew is discovered early enough, old household remedies such as milk and baking soda often help, but you should use them several times at intervals of a few days. Unfortunately, a single application does not have the desired effect.

    Splash with milk

    youtube

    For this tried and tested recipe, use fresh, natural whole milk or just as fresh buttermilk as possible. Just like UHT milk, low-fat milk is unsuitable and does not show the desired success, since the enzymes and bacteria present in the milk for the treatment were killed by the previous treatment. And that's how it works:

    1. Mix the fresh milk with boiled (let cool!) water.
    2. The ratio should be 1:9 (1 part milk, 9 parts water) or 1:7.
    3. If possible, use rainwater or stagnant tap water.
    4. Pour the mixture into a previously thoroughly cleaned spray bottle.
    5. Thoroughly spray the affected parts of the plant.
    6. The liquid should drip from the leaves and shoots.
    7. Don't forget to treat the underside of the leaves as well.

    Repeat the spray treatment every two to three days for a period of two to three weeks.

    Baking powder against mildew

    Baking soda is great for fighting mildew

    Strictly speaking, the remedy for powdery mildew is not baking powder here, but baking soda. This, in turn, is not included in every baking powder, so you should take a closer look at the list of ingredients beforehand. Mix one packet of baking soda (or baking soda) with 20 milliliters of canola or sunflower oil and two liters of water. Pour the mixture into a previously cleaned spray bottle and treat the plants affected by powdery mildew several times a week.

    digression

    Beneficial insects against powdery mildew

    The larvae of some ladybird species literally graze on mildew and can therefore be used to combat the plant disease. This applies above all to the two-spot ladybird and the twenty-two-spot ladybird (which in turn is popularly known as the mushroom ladybird for a reason).

    Strengthen plants with homemade liquid manure

    Plant manure, known as “fermented extract” in technical jargon, is not only a wonderful fertilizer that is easy to make, but also prevents the development of fungal diseases. Fermented extracts provide everything that is important for plant health and help to strengthen the plant's natural defences. When it comes to upgrading garden plants against fungal diseases, horsetail is your best bet. But other basic ingredients, such as garlic, nettle or tansy, are also suitable.

    However, plant manure as a spray only works preventively or in the early stages of mildew infestation. If the disease is already more advanced, you have to bring out the heavier artillery. Therefore, water your (endangered) garden plants regularly with home-made extracts between April and August to prevent infection. In order for the concoction to be actually effective, it is important to observe the following basic rules:

    • Use rain or spring water.
    • Insert fresh, finely chopped plant material.
    • Make each extract separately.
    • Pay attention to the right temperature.
    • Don't make too small batches, it's more difficult.
    • Stir once a day.
    • Check on your preparation at least once a day, don't leave it unattended for too long.
    • Use a fine filter (e.g. cheesecloth) to strain.
    • Once the extract is ready, start using it immediately.

    Horsetail against powdery mildew

    Horsetail can be found everywhere along the way

    Horsetail broth is primarily effective against powdery mildew pathogens, which is mainly due to the mineral salts it contains, such as silica, potassium and calcium. These make the plants more resistant to fungal and insect attacks. Used preventively against powdery mildew and other fungal diseases, you should dilute the broth to ten percent. This corresponds to a mixing ratio of one part liquid manure and nine parts water.

    Recipe:

    1. Gather a kilogram of marsh or field horsetail without roots.
    2. Give preference to field horsetail, as it contains a particularly large amount of silica. However, swamp horsetail is easier to find.
    3. Cut the horsetail as finely as possible, as this will release the silica better.
    4. Place the plant material in a plastic bucket.
    5. Now pour in ten liters of water and stir well.
    6. Horsetail should be stirred twice a day to allow the plants to soak up water.
    7. Depending on the outside temperature, fermentation lasts between eight and 14 days.

    As soon as there are no more bubbles, filter the manure and fill it into suitable, well-closable containers. Spray the plants with the diluted remedy about every eight to 10 days between spring and August.

    Garlic against powdery mildew

    Garlic is a real all-rounder as a plant protection agent. The allium plant not only helps against all kinds of plant fungal diseases, but also as an insecticide or insect repellent against one or the other garden pest. The following recipe in particular has proven to be particularly effective for these applications:

    1. Crush, crush or chop 100 grams of fresh garlic with the skin on.
    2. Mix this with three tablespoons of canola or sunflower oil.
    3. Cover and let the mixture steep for about 24 hours.
    4. Then strain the liquid.
    5. Crush the garlic flesh to extract as many active ingredients as possible from the bulb.
    6. Add a tablespoon of soft soap (€44.90) or washing-up liquid.
    7. Stir well with a whisk.
    8. Pour the mixture with a liter of water.

    Refrigerated and protected from the sun, this preparation will keep for about three weeks. As a fungicide - in addition to mildew, the extract is also effective against rust, botrytis and other fungal diseases - dilute the agent in a ratio of 1:20 with water.

    Nettle against powdery mildew

    The stinging nettle, abused by many as an annoying weed, is also one of the versatile all-rounders in the garden. With its high nitrogen and iron content, the plant is very suitable as a fertilizer. It can also be used as an insecticide, to protect against plant pests and as a fungicide. Harvest the plant before flowering, as this is when the active ingredient content is at its highest. Be sure to wear gloves! The stinging nettle can be used fresh or - if you have some available - dried. Stinging nettle plants can be dried quickly by spreading them out in a dry and light-protected place.

    Recipe and application:

    1. Allow one kilogram of fresh plant material (roots, leaves and stems) to ferment in ten liters of water for eight to ten days.
    2. Proceed as described in the recipe for making horsetail manure.
    3. Dilute the finished manure with water in a ratio of 1:10.
    4. Use it as a spray, which can be applied preventively every two weeks.

    This video explains how to make nettle manure and what else it is good for:youtube

    Tansy against downy mildew

    Tansy (lat. Tanacetum vulgare) is ideal in the form of an infusion against downy mildew. The tansy with its fine, light green leaves and its intense smell has always been used as a plant protection product. It blooms in yellow, firm flower heads all summer long. Tansy likes to stand in sunny places and loves nutrient-rich, rather moist soil.

    To make an infusion, pour 1 liter of hot water over 100 grams of fresh flower heads (or 20 grams of dried ones). This should no longer boil. Let the mixture steep until it cools to room temperature. Now strain the brew and dilute it with water in a ratio of 1:5. Incidentally, tansy is also suitable as a spray against rust diseases or plant pests such as aphids.

    tips

    In contrast to fermented extracts (manure), infusions do not keep and must therefore be used immediately.

    Oregano against downy mildew

    A great home remedy for powdery mildew can be made from oregano

    Oregano or real Dost (lat. Origanum vulgare), as the herb found almost everywhere in Europe is also known, does not only taste good in tomato sauce. Instead, you can also use the herb against fungal diseases in plants. Oregano prefers to grow in warm, dry locations with a calcareous subsoil. You also need extra-fine clay, as the oregano essential oils then stick to the plants better.

    Oregano Fungicide Recipe:

    1. Gather 100 grams of fresh oregano before flowering.
    2. Use stems and leaves.
    3. Cut the herb as finely as possible.
    4. Mix the material with a tablespoon of canola or sunflower oil.
    5. Let the mixture steep for 24 hours.
    6. Then strain out the liquid.
    7. Add three to four drops of liquid dish soap.
    8. Finally, mix the mixture with 250 milliliters of water to form a homogeneous liquid.
    9. In another container, make a clay-water mixture.
    10. Take a teaspoon of fine clay and a liter of water.
    11. Finally, fill both liquids together in a spray bottle.
    12. Shake the mixture thoroughly.

    Apply spray as needed.

    digression

    Do Microbes Actually Help Against Powdery Mildew?

    Of course, microbes living in the soil, such as the fungus Ampelomyces quisqualis or the bacterium Bacillus subtilis, do not help once powdery mildew has already broken out. Instead, you should use them to prevent them, because these microorganisms ensure a balanced and healthy balance in the soil. This in turn benefits the plants growing on it and strengthens their immune system - so pathogens hardly have a chance. You can obtain soil-activating microbes from specialist retailers.

    Suitable pesticides for heavy infestations

    Sometimes, however, the only thing that really helps is to use chemical pesticides, because mildew is very difficult to combat in some years. Suitable agents usually work on the basis of sulfur or copper, which kill the pathogens immediately on contact. These are so-called contact fungicides. Typically, the agents also penetrate the plants and act where surface-sprayed plant protection agents cannot reach.

    Nevertheless, you should think carefully about the application, because the use of such agents always has negative consequences. For example, the chemicals pollute the soil and upset the natural balance. Quite apart from the fact that the active ingredients can get into the groundwater. In addition, the funds naturally also have a serious impact on other plants and animals in the garden. An alternative are biological preparations (e.g. "fungus-free").

    frequently asked Questions

    Can I actually use any baking powder to combat powdery mildew?

    No! It is not the baking powder itself that is effective against mildew, but the baking soda contained in some varieties. Cream of tartar, for example, is not suitable for combating the fungal disease. Instead, you can also use baking soda or baking soda.

    Is powdery mildew also dangerous for humans?

    In principle, the fungus and its spores are poisonous to humans, although healthy people usually feel little or no effect - parts of plants infected with powdery mildew should not be eaten anyway, as the taste also suffers from the infection. It becomes more of a problem if you are allergic to fungi - and especially penicillin. In this case you have to reckon with corresponding allergic reactions.

    How can I prevent powdery mildew on roses?

    You cannot completely prevent a powdery mildew infection on roses, after all, it is not without reason that the "queen of flowers" is considered to be particularly susceptible to the disease. However, you can reduce the likelihood of disease by planting mildew-resistant varieties (so-called ADR roses), ensuring an optimal location and proper care and also treating the roses preventively with plant strengtheners, such as home-made plant manure based on horsetail, nettle or tansy.

    What does mildew resistant actually mean?

    Types of plants that are resistant to the pathogens of this disease and do not become ill as quickly as other varieties are referred to as mildew-resistant or mildew-tolerant (especially certain rose varieties). However, this does not usually mean that these plants can never become ill. Only the probability of illness is lower.

    Is powdery mildew contagious to other garden plants?

    Powdery mildew is also highly contagious for other garden plants, which is why an infestation must be treated immediately. For this reason, do not make the mistake of throwing cut, infected plant parts on the compost. The fungal spores survive here and are eventually also spread in the garden when the finished compost is spread. Therefore, such clippings always belong in the household waste or should be burned.

    tips

    When pruning in the garden, you should thoroughly clean and disinfect the tools you use with alcohol before using them on other plants. In this way you prevent an infection with powdery mildew via this transmission route.

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